frequently asked questions

Important Question, Ask By Client

During selection of filter bag media, basic parameters taken into consideration are

1. inlet gas temperature, 2. % moisture contents in flue gasses , inlet dust load & it’s characteristics.

For non woven filter bags, 8-16 vertical wires cages are to be used, with smooth surface finsih either with galvanizing or painted. In case of membrane bags minimum 16-24 vertical wire cages are selected. Again a smooth surface finish is a prime requirement of any filter bag to perform to it’s desire life.
To get optimum / best performance, for non woven[ felt] bags… bag ID to cage OD…. a pinch should be 7-9 mm, and in case of glass or glass with membrane bags max. pinch should be 3.5 to 4.5 mm.

Normally for all types of non woven bags, cleaning pressure of 5-7 kg/cm2 to be kept.[ It also depends on bag length & dia ],For non woven membrane bags, glass or glass with membrane bags cleaning pressure should be in between 3-3.5 kg/cm2.

If pressure in both cases will be more than above mentioned values then bags will get less life & chances of pre-mature failure or carry over of fine dust in bag filter, results into high DP.

DP mode, it is “ on demand “ cleaning of bags. When DP across bag filter increases to it’s set upper limit, cleaning will start & when DP drops down below set limit then cleaning will stop.

In time mode, it is continuous & cleaning program will start as soon as bag filter will be in operation.

In DP mode, bag life will enhance, as compare to time mode.

All membrane non woven & woven fabric bags operates on a principle of surface filtration where micro fine particles will not pass through membrane lamination hence nearly zero emission.

Moreover, membrane laminated bags will require less pressure as compare to conventional fabric media bags , so less mechanical stress or flexing of fabric hence more bag life.

Any new bag when it is installed should be pre-coated. This will protect mother fabric from unwanted chemical reaction of gases generated in process. A fine pre-coat layer of dust over bag surface is a main reason of developing dust cake over the bag.

In some cases, it is not practically possible to pre-coat bags by external dust. In such cases, installed bags can be pre- coated with dust which is a process dust generated during operation of bag filter. So unless pressure drop across bag filter reaches to 100 mmWC, then only cleaning cycle programmer to be started.

When DP of bag filter is beyond 150 mmWC, then it is consider HIGH DP. The main reasons of high DP is either sudden increase of inlet dust load or gas flow handled by bag filter is more than design flow or generation of fines are more in inlet dust or ineffective cleaning of bags due to wrong cleaning program timing settings.

When pollution control board requirements of emission less than 30 mg/nm3 or in process fine particles less than 5 microns size are more than 15 % .

The reason for puffing during cleaning of bags is due to insufficient pre-coat layer over the bags, or excessive cleaning pressure or bags stitching holes gets open while high cleaning pressure. It is also due to improper settings of cleaning cycle programmer timings.
After opening tube sheet covers, near to torn bag a huge amount of dust settlement you will notice. If any bag is having small pin hole [ 5-10 mm dia ] & gives visible emission then check on manifold pipe a dust impressions or marks near to holes in manifold pipe.

Any failure of bag, categories under three sections 1. Failure due to mechanical 2 failure due to long lasted excessive / surge temperature 3. Fabric chemically reacted with sudden changes in process gas composition.

IFF is having well equipped test lab and R & D center facility to find out and pin point root cause with conclusion . We can also tell you residual bag life left.

The membrane lamination over non woven & woven fabric is thin micro porous film which is thermo bonded over the base mother fabric media. Since it is a ePTFE thin film & there could be chances of getting even invisible hair crack on membrane surface by any sharp edge object, thimble burrs or sharp edges in cages, during bags installation. So IFF always recommends to use a protected sleeve while installing membrane bags.